In trench isolated integrate circuits, a known problem has been that of stress caused by the dielectric fill in the trench on the silicon substrate. U.S. Pat. No. 4,631,803 illustrates a set of different liners that are used to relief the stress. One example is an oxide-nitride (ON) layer, another example is a triple layer of oxide-nitride-oxide (ONO). This and other references illustrate a rather thick layer of oxide in the range of 20-45 nm and a relatively thick layer of nitride in the range of 30-60 nm. Another article "Oxidation-Induced Defect Generation in Advanced DRAM Structures" by S. R. Stiffler, et al. in IEEE Transactions on Electron Devices, Vol. 37, No. 5, May 1990 illustrates a relatively thin layer of nitride of thickness 7 nm.
A problem with this and other nitride liners in the art is that when a conventional stripping process of hot phosphoric acid is used to strip the protective pad nitride that coats the wafer, the phosphoric acid recesses the nitride liner, exposing a gap. Subsequent etches in hydrofluoric acid cause that recess to expand into an unacceptably large void.